1. Field
The present disclosure generally relates to fabrication of composite laminate stiffeners, and deals more particularly with a method and device for producing contoured stiffeners which reduce ply wrinkling.
2. Background
Contoured composite laminate stiffeners such as concave shaped stringers may be fabricated using a combination of primary and secondary forming operations. For example, punch forming may be used to form a flat composite charge into a straight stiffener having a desired cross sectional shape such as, without limitation, a hat-shaped cross section. In a secondary forming operation, the stringer is formed along its length onto a curved forming tool using a substantially straight, semi-flexible compactor having a hat-shaped cross section. Atmospheric pressure applied to the compactor through a vacuum bag, and optionally, autoclave pressure, forms the stiffener onto the curved forming tool, imparting the desired curvature to the stiffener. During the secondary forming operation, bending strain is generated within the stiffener as it conforms to the contour of the forming tool. This bending strain may cause local buckling of the composite fibers in the green laminate, producing undesired wrinkling in the cured part, particularly in areas near the inside radius of the contoured stiffener.
Accordingly, there is a need for a method and device for reducing laminate wrinkling during contouring of composite laminate stiffeners by controlling in-plane strain in those areas of the laminate that may be subject to buckling.